【Line】 , 【row】 , 【rank】 , 【file】 , 【echelon】 , 【tier】 are comparable when meaning a series of things arranged in continuous or uniform order.
【Line】 means little more than this, except when it is attached to a specific application that increases its implications; thus, a 【line】 of type may equal a 【line】 of poetry, but there is a wealth of implication in the second that is absent from the first.
【Row】 may suggest one 【line】 or one of several parallel lines; it is applicable to lines composed of persons or of things whether they range horizontally or vertically or abreast or away from one.
【Rank】 and 【file】 are found chiefly in military use, 【rank】 denoting a 【row】 of men side by side, 【file】 a 【row】 of men one behind another. The conjoined use of these terms in 【rank】 and 【file】 is an idiomatic extension meaning the masses of men as distinguished from their leaders or rulers.
【Echelon】 usually implies a regular arrangement or formation in which each unit (as one of a series of parallel ranks of troops or one of a fleet of vessels headed in the same direction) is a little to the left or to the right of the unit immediately behind.
【Tier】 applies to one of a set of rows arranged one above another; it occasionally refers to persons but usually deals with parts of a structure or framework which are repeated.
